18:1 AFR is "cleaner"?
 

So, assuming the catalyst is fully warmed-up, doesn't a graph such as this indicate that an AFR of 18:1 is better for emissions than stoich? I realize we can only be in lean burn under light throttle and load conditions. Nonetheless, at 18:1 only 02 is higher than at 14.7:1. That seems gooder for everybody. So 18:1 is simply better, no? Why aren't all cars in lean burn under light load and part throttle and steady cruise on freeways?

https://ecomodder.com/forum/member-c...-4gaschart.gif

Probably because of the nox spike at 16:1. They appear to be concerned about the nox most.

That makes sense, but at 18:1 NOx is lower than at stoich and much lower than 16:1. So assuming an efficient catalyst, less NOx going into the catalyst means less coming out the tailpipe, no?

The EPA declared war on NOx and the government want us all to buy more gallons of fuel.

Again though, at 18:1 AFR, this chart suggests NOx is lower than at 14.7:1 and so is CO2. Why isn't 18:1 lean burn common place in contemporary cars? Or is it maybe common and not touted like in the old days of the 90s and early 00s?

That graph is assuming you don’t have a cat,

Given the circumstances today it’s likely because of two things

1. We never did it so it’s impossible (hear that a lot)
2. Emissions controls (not represented by the graph) reduce Nox below the graph,

the unfortunate part is because we are laser focused are a single pollution percentage we rather burn more fuel and make more pollution in grams per mile.

Oh its too difficult for obsolete binary O2 sensors to detect and maintain 18:1 and it was decided that stoich was cleaner not with actual science, but with politics.
And most importantly it burns more fuel.

Doesn't the cat have overtemp isses when too much air is introduced?

I am aware that the graph assumes no CAT. But if the exhaust in cleaner going in, it'll be cleaner coming out, assuming a properly efficient CAT, right? Am I wrong about that? Cleaner in, means cleaner out?

This all would suggest that modifying a car to run lean at 18:1 is likely cleaner than stock. Hondas like the VX and HX and the Insight all did lean burn from 1992-2006 and they had the best or almost best emissions ratings (LEV, ULEV, and such). Those lean burn systems relied merely on ECU tuning, a wideband O2, and a knock sensor, IIRC. Not a super high bar.

I guess I am surprised because I thought the LB engines had higher NOx, but that is no necessarily true, unless something is still missing from this picture.

That is the kind of thing I cannot find clear answers for online. I see contradictory things... some say lean burn makes the catalyst cooler.